1. Field of the Invention
The present invention relates to a method of manufacturing a toner, a toner, a two-component developer, a developing device, and an image forming apparatus.
2. Description of the Related Art
Toners for visualizing latent images have been used in various image forming processes and, as an example thereof, an electrophotographic method has been known.
An electrophotographic image forming apparatus includes a photoreceptor, a charging section which charges the surface of the photoreceptor, an exposure section which irradiates the surface of the photoreceptor in a charged state with a signal light to form an electrostatic latent images corresponding to image information, a developing section which supplies a toner in a developer to electrostatic latent images on the surface of the photoreceptor to form toner images, a transfer section having a transfer roller which transfers the toner images on the surface of the photoreceptor to a recording medium, a fixing section having a fixing roller which fixes the toner images onto the recording medium, and a cleaning section which cleans the surface of the photoreceptor after the transfer of the toner images, and the image forming apparatus develops the electrostatic latent images by a one-component developer containing a toner as a developer or by a two-component developer containing a toner and a carrier to form images. Since the electrophotographic image forming apparatus can form images of good image quality at high speed and at a low cost, the apparatus is utilized, for example, in copying machines, printers, and facsimile units and recent popularization thereof is remarkable. Correspondingly, a demand for the image forming apparatus has become severer. Among all, an importance is attached particularly to high definition, high resolution, and stabilization of image quality formed by the image forming apparatus, and increase in the image forming speed. For attaining them, studies on both of the image forming process and the developer has become indispensable.
For obtaining higher definition and higher resolution of images, decrease in size of the toner particle is one of subjects to be solved regarding the developer with a view point that reproduction of electrostatic latent images at high fidelity and high accuracy is important. The toner particle is generally a resin particle in which a colorant, a wax as a release agent, etc. are dispersed in a binder resin as a matrix. In a general production method for small-sized toner particle, it is generally difficult to decrease the size of the wax dispersed in the binder resin. Accordingly, there is a problem that the wax bleeds out with time from the manufactured small-sized toner particle to cause filming to the photoreceptor. Further, a great amount of the wax bleeds out to the surface of the toner particle and, particularly, at a high temperature, the wax is melted to exhibit tackiness. As a result, an offset phenomenon that the toner is not transferred or fixed to a recording medium but the toner is attached to a transfer roller, a fixing roller, etc. tends to occur frequently.
As a method of decreasing the size of the wax, a method of manufacturing a toner including at least a mixing step of mixing 100 parts by weight of a thermoplastic resin and 1 to 7 parts by weight of a wax, a melt-kneading step of melt-kneading a mixture obtained in the mixing step in which the melt-kneading temperature is within a range: (Tm−20)° C. to (Tm+20)° C. (Tm is a melting temperature of thermoplastic resin), and the temperature of the melt-kneaded product after melt-kneading is (Tm+35)° C. or lower, and a pulverizing and classifying step of cooling, pulverizing and classifying a melt-kneaded product obtained in the melt-kneading step has been proposed (for example, refer to Japanese Unexamined Patent Publication JP-A 6-161153 (1994)). Further, a method of manufacturing a toner of melt-kneading a toner raw material mixture and cooling, pulverizing, and classifying the obtained melt-kneaded product in which the toner raw material mixture is melt-kneaded by using a kneading extrusion device where a downwardly inclined slide-like discharge portion is in adjacent with an outlet of a cylinder portion having, at the inside, a kneading conveying member for kneading and conveying the toner raw material mixture has been proposed (for example, in Japanese Unexamined Patent Publication JP-A 9-277348 (1997)).
The manufacturing methods described above intend to prevent the occurrence of filming to a photoreceptor and the offset phenomenon due to the bleed-out of the wax as the size of the wax contained in the toner particle is decreased. However, since the methods are basically a melt-kneading method known so far, while decrease in size of the wax can be attained, this does not contribute to sufficient decrease in size of the toner particle per se. Accordingly, obtained toner particle is not sufficiently satisfactory in view of the image reproducibility, particularly, definition and resolution.
On the other hand, an emulsifying dispersion apparatus including an emulsifying dispersion section, a conduit channel, a heat exchange section, and a multistage depressurizing section has been proposed,(for example, refer to International Publication WO03/059497). The emulsifying dispersion section prepares a liquid emulsion by emulsifying and dispersing an emulsifying material in a liquid as a matrix by a shearing force. The conduit channel supplies a pressurized liquid emulsion obtained by the emulsifying dispersion section to the multistage depressurizing section. The heat exchange section is disposed on the conduit channel to cool the liquid emulsion. The multistage depressurizing section discharges the liquid emulsion after reducing the pressure of the liquid emulsion supplied from the conduit channel to such a level as causing no bubbling even when the liquid emulsion is discharged into an atmospheric pressure. The emulsifying dispersion apparatus at first prepares a liquid emulsion in which the emulsifying material is dispersed uniformly by dispersing the emulsifying material under pressure into the liquid. Then, the apparatus reduces the pressure of the liquid emulsion stepwise and reduces the pressure finally to such an extent of pressure as causing no bubbling. It intends to prevent the particles of the emulsifying material dispersed in the liquid emulsion from growing thereby obtaining a liquid emulsion in which particles of the emulsifying material of a uniform particle size are dispersed. According to the emulsifying dispersion apparatus, since high shearing force can be applied in the emulsifying dispersion section by the provision of the multistage depressurizing section, an emulsion, for example, of water and oil can be manufactured easily. However, in a case of manufacturing toner particles by the apparatus, control for the particle size is difficult to result in a problem that toner particles of a desired small size cannot be obtained. Further, WO03/059497 does not suggest at all not only that the size of the toner particles is to be decreased but also that a toner where a wax of a smaller size than that of the toner particle dispersed uniformly in the toner particles is to be obtained. Further, WO 03/059497 has no description for applying the emulsifying dispersion apparatus to the manufacture of the toner particles.